rfc2328.txt

来自「中、英文RFC文档大全打包下载完全版 .」· 文本 代码 · 共 1,379 行 · 第 1/5 页

Network Working Group                                             J. Moy
Request for Comments: 2328                   Ascend Communications, Inc.
STD: 54                                                       April 1998
Obsoletes: 2178
Category: Standards Track


                             OSPF Version 2


Status of this Memo

    This document specifies an Internet standards track protocol for the
    Internet community, and requests discussion and suggestions for
    improvements.  Please refer to the current edition of the "Internet
    Official Protocol Standards" (STD 1) for the standardization state
    and status of this protocol.  Distribution of this memo is
    unlimited.

Copyright Notice

    Copyright (C) The Internet Society (1998).  All Rights Reserved.

Abstract

    This memo documents version 2 of the OSPF protocol.  OSPF is a
    link-state routing protocol.  It is designed to be run internal to a
    single Autonomous System.  Each OSPF router maintains an identical
    database describing the Autonomous System's topology.  From this
    database, a routing table is calculated by constructing a shortest-
    path tree.

    OSPF recalculates routes quickly in the face of topological changes,
    utilizing a minimum of routing protocol traffic.  OSPF provides
    support for equal-cost multipath.  An area routing capability is
    provided, enabling an additional level of routing protection and a
    reduction in routing protocol traffic.  In addition, all OSPF
    routing protocol exchanges are authenticated.

    The differences between this memo and RFC 2178 are explained in
    Appendix G. All differences are backward-compatible in nature.




Moy                         Standards Track                     [Page 1]

RFC 2328                     OSPF Version 2                   April 1998


    Implementations of this memo and of RFCs 2178, 1583, and 1247 will
    interoperate.

    Please send comments to [e-mail].

Table of Contents

    1        Introduction ........................................... 6
    1.1      Protocol Overview ...................................... 6
    1.2      Definitions of commonly used terms ..................... 8
    1.3      Brief history of link-state routing technology ........ 11
    1.4      Organization of this document ......................... 12
    1.5      Acknowledgments ....................................... 12
    2        The link-state database: organization and calculations  13
    2.1      Representation of routers and networks ................ 13
    2.1.1    Representation of non-broadcast networks .............. 15
    2.1.2    An example link-state database ........................ 18
    2.2      The shortest-path tree ................................ 21
    2.3      Use of external routing information ................... 23
    2.4      Equal-cost multipath .................................. 26
    3        Splitting the AS into Areas ........................... 26
    3.1      The backbone of the Autonomous System ................. 27
    3.2      Inter-area routing .................................... 27
    3.3      Classification of routers ............................. 28
    3.4      A sample area configuration ........................... 29
    3.5      IP subnetting support ................................. 35
    3.6      Supporting stub areas ................................. 37
    3.7      Partitions of areas ................................... 38
    4        Functional Summary .................................... 40
    4.1      Inter-area routing .................................... 41
    4.2      AS external routes .................................... 41
    4.3      Routing protocol packets .............................. 42
    4.4      Basic implementation requirements ..................... 43
    4.5      Optional OSPF capabilities ............................ 46
    5        Protocol data structures .............................. 47
    6        The Area Data Structure ............................... 49
    7        Bringing Up Adjacencies ............................... 52
    7.1      The Hello Protocol .................................... 52
    7.2      The Synchronization of Databases ...................... 53
    7.3      The Designated Router ................................. 54
    7.4      The Backup Designated Router .......................... 56
    7.5      The graph of adjacencies .............................. 56



Moy                         Standards Track                     [Page 2]

RFC 2328                     OSPF Version 2                   April 1998


    8        Protocol Packet Processing ............................ 58
    8.1      Sending protocol packets .............................. 58
    8.2      Receiving protocol packets ............................ 61
    9        The Interface Data Structure .......................... 63
    9.1      Interface states ...................................... 67
    9.2      Events causing interface state changes ................ 70
    9.3      The Interface state machine ........................... 72
    9.4      Electing the Designated Router ........................ 75
    9.5      Sending Hello packets ................................. 77
    9.5.1    Sending Hello packets on NBMA networks ................ 79
    10       The Neighbor Data Structure ........................... 80
    10.1     Neighbor states ....................................... 83
    10.2     Events causing neighbor state changes ................. 87
    10.3     The Neighbor state machine ............................ 89
    10.4     Whether to become adjacent ............................ 95
    10.5     Receiving Hello Packets ............................... 96
    10.6     Receiving Database Description Packets ................ 99
    10.7     Receiving Link State Request Packets ................. 102
    10.8     Sending Database Description Packets ................. 103
    10.9     Sending Link State Request Packets ................... 104
    10.10    An Example ........................................... 105
    11       The Routing Table Structure .......................... 107
    11.1     Routing table lookup ................................. 111
    11.2     Sample routing table, without areas .................. 111
    11.3     Sample routing table, with areas ..................... 112
    12       Link State Advertisements (LSAs) ..................... 115
    12.1     The LSA Header ....................................... 116
    12.1.1   LS age ............................................... 116
    12.1.2   Options .............................................. 117
    12.1.3   LS type .............................................. 117
    12.1.4   Link State ID ........................................ 117
    12.1.5   Advertising Router ................................... 119
    12.1.6   LS sequence number ................................... 120
    12.1.7   LS checksum .......................................... 121
    12.2     The link state database .............................. 121
    12.3     Representation of TOS ................................ 122
    12.4     Originating LSAs ..................................... 123
    12.4.1   Router-LSAs .......................................... 126
    12.4.1.1 Describing point-to-point interfaces ................. 130
    12.4.1.2 Describing broadcast and NBMA interfaces ............. 130
    12.4.1.3 Describing virtual links ............................. 131
    12.4.1.4 Describing Point-to-MultiPoint interfaces ............ 131



Moy                         Standards Track                     [Page 3]

RFC 2328                     OSPF Version 2                   April 1998


    12.4.1.5 Examples of router-LSAs .............................. 132
    12.4.2   Network-LSAs ......................................... 133
    12.4.2.1 Examples of network-LSAs ............................. 134
    12.4.3   Summary-LSAs ......................................... 135
    12.4.3.1 Originating summary-LSAs into stub areas ............. 137
    12.4.3.2 Examples of summary-LSAs ............................. 138
    12.4.4   AS-external-LSAs ..................................... 139
    12.4.4.1 Examples of AS-external-LSAs ......................... 140
    13       The Flooding Procedure ............................... 143
    13.1     Determining which LSA is newer ....................... 146
    13.2     Installing LSAs in the database ...................... 147
    13.3     Next step in the flooding procedure .................. 148
    13.4     Receiving self-originated LSAs ....................... 151
    13.5     Sending Link State Acknowledgment packets ............ 152
    13.6     Retransmitting LSAs .................................. 154
    13.7     Receiving link state acknowledgments ................. 155
    14       Aging The Link State Database ........................ 156
    14.1     Premature aging of LSAs .............................. 157
    15       Virtual Links ........................................ 158
    16       Calculation of the routing table ..................... 160
    16.1     Calculating the shortest-path tree for an area ....... 161
    16.1.1   The next hop calculation ............................. 167
    16.2     Calculating the inter-area routes .................... 178
    16.3     Examining transit areas' summary-LSAs ................ 170
    16.4     Calculating AS external routes ....................... 173
    16.4.1   External path preferences ............................ 175
    16.5     Incremental updates -- summary-LSAs .................. 175
    16.6     Incremental updates -- AS-external-LSAs .............. 177
    16.7     Events generated as a result of routing table changes  177
    16.8     Equal-cost multipath ................................. 178
             Footnotes ............................................ 179
             References ........................................... 183
    A        OSPF data formats .................................... 185
    A.1      Encapsulation of OSPF packets ........................ 185
    A.2      The Options field .................................... 187
    A.3      OSPF Packet Formats .................................. 189
    A.3.1    The OSPF packet header ............................... 190
    A.3.2    The Hello packet ..................................... 193
    A.3.3    The Database Description packet ...................... 195
    A.3.4    The Link State Request packet ........................ 197
    A.3.5    The Link State Update packet ......................... 199
    A.3.6    The Link State Acknowledgment packet ................. 201



Moy                         Standards Track                     [Page 4]

RFC 2328                     OSPF Version 2                   April 1998


    A.4      LSA formats .......................................... 203
    A.4.1    The LSA header ....................................... 204
    A.4.2    Router-LSAs .......................................... 206
    A.4.3    Network-LSAs ......................................... 210
    A.4.4    Summary-LSAs ......................................... 212
    A.4.5    AS-external-LSAs ..................................... 214
    B        Architectural Constants .............................. 217
    C        Configurable Constants ............................... 219
    C.1      Global parameters .................................... 219
    C.2      Area parameters ...................................... 220
    C.3      Router interface parameters .......................... 221
    C.4      Virtual link parameters .............................. 224
    C.5      NBMA network parameters .............................. 224
    C.6      Point-to-MultiPoint network parameters ............... 225
    C.7      Host route parameters ................................ 226
    D        Authentication ....................................... 227
    D.1      Null authentication .................................. 227
    D.2      Simple password authentication ....................... 228
    D.3      Cryptographic authentication ......................... 228
    D.4      Message generation ................................... 231
    D.4.1    Generating Null authentication ....................... 231
    D.4.2    Generating Simple password authentication ............ 232
    D.4.3    Generating Cryptographic authentication .............. 232
    D.5      Message verification ................................. 234
    D.5.1    Verifying Null authentication ........................ 234
    D.5.2    Verifying Simple password authentication ............. 234
    D.5.3    Verifying Cryptographic authentication ............... 235
    E        An algorithm for assigning Link State IDs ............ 236
    F        Multiple interfaces to the same network/subnet ....... 239
    G        Differences from RFC 2178 ............................ 240
    G.1      Flooding modifications ............................... 240
    G.2      Changes to external path preferences ................. 241
    G.3      Incomplete resolution of virtual next hops ........... 241
    G.4      Routing table lookup ................................. 241
             Security Considerations .............................. 243
             Author's Address ..................................... 243
             Full Copyright Statement ............................. 244








Moy                         Standards Track                     [Page 5]

RFC 2328                     OSPF Version 2                   April 1998


1.  Introduction

    This document is a specification of the Open Shortest Path First
    (OSPF) TCP/IP internet routing protocol.  OSPF is classified as an
    Interior Gateway Protocol (IGP).  This means that it distributes
    routing information between routers belonging to a single Autonomous
    System.  The OSPF protocol is based on link-state or SPF technology.
    This is a departure from the Bellman-Ford base used by traditional
    TCP/IP internet routing protocols.

    The OSPF protocol was developed by the OSPF working group of the
    Internet Engineering Task Force.  It has been designed expressly for
    the TCP/IP internet environment, including explicit support for CIDR
    and the tagging of externally-derived routing information.  OSPF
    also provides for the authentication of routing updates, and
    utilizes IP multicast when sending/receiving the updates.  In
    addition, much work has been done to produce a protocol that
    responds quickly to topology changes, yet involves small amounts of
    routing protocol traffic.

    1.1.  Protocol overview